Nitric oxide (NO) is crucial to many biological systems, and is known to mediate the control of blood pressure, help the immune system kill invading parasites that enter cells, inhibit division of cancer cells, transmit signals between brain cells, and contribute to the large scale death of brain cells that can debilitate people with strokes or Huntington's disease. Nitric oxide also mediates relaxation of smooth muscle present, for example, in the walls of the blood vessels, bronchi, gastrointestinal tract, and urogenital tract. Administration of nitric oxide gas to the lung by inhalation has been shown to produce localized smooth muscle relaxation to treat bronchial constriction and pulmonary hypertension, pneumonia, etc. in adults and children without systemic side effects.
Inhaled nitric oxide is a potent local pulmonary vasodilator and bronchodilator that improves the matching of ventilation with perfusion, thereby increasing the injured lungs oxygen transport efficiency and raising the arterial oxygen tension. Nitric oxide combines a rapid onset of action occurring within seconds with the absence of systemic vasodilatory effects. Once inhaled, it diffuses through the pulmonary vasculature into the bloodstream, where it is rapidly inactivated by combination with hemoglobin. Therefore, the bronchodilator effects of inhaled nitric oxide are limited to the airway and the vasodilatory effects of inhaled nitric oxide are limited to the pulmonary vasculature. The ability of nitric oxide to dilate pulmonary vessels selectively provides therapeutic advantages in the treatment of acute and chronic pulmonary hypertension.
U.S. Pat. No. 5,396,882 to Zapol, which is incorporated by reference herein, describes electric generation of nitric oxide (NO) from air at ambient pressure for medical purposes. As described in U.S. Pat. No. 5,396,882, an air input port of the system is used for continuously introducing air into the electric arc chamber. Unwanted by-products formed during the production of NO (e.g., nitrogen dioxide (NO2) and ozone (O3)) are absorbed, for example, by a scavenger or catalytic converter before the electrically generated NO is used for medical purposes.
NO oxidizes in an oxygen-containing atmosphere to form NO2. NO2 is a toxic by-product which forms nitric acid when dissolved in airway secretions or cells. Generating NO with low levels of NO2 is often desirable.